In a particle-beam exposure apparatus, a particle beam is generated by an illumination system and illuminates a pattern definition means having an array of apertures which define a beam pattern to be projected on a target surface. One important application of a particle-beam exposure apparatus of this kind is in the field of nano-scale patterning, by direct ion beam material modification or by electron or ion beam induced etching and/or deposition, used for the fabrication or functionalization of nano-scale devices. Another important application is in the field of maskless particle-beam lithography, used in semiconductor technology; namely, a lithography apparatus which, in order to define a desired pattern on a substrate surface, processes a substrate, e.g. a silicon wafer, covered with a layer of a radiation-sensitive resist. A desired structure is exposed onto the photo-resist which is then developed, in the case of a positive resist by partial removal according to the pattern defined by the previous exposure step. The developed resist is used as a mask for further structuring processes such as reactive etching.
A particle-beam exposure apparatus is described in the U.S. Pat. No. 5,369,282. Arai et al. therein discuss an electron-beam exposure system using a so-called blanking aperture array (BAA) which takes the role of the pattern definition means. The BAA carries a number of rows of apertures, and the images of the apertures are scanned over the surface of the substrate in a controlled continuous motion whose direction is perpendicular to the aperture rows. The rows are aligned with respect to each other in an interlacing manner so that the apertures form staggered lines as seen along the scanning direction. Thus, the staggered lines sweep continuous lines on the substrate surface without leaving gaps between them as they move relative to the substrate, thus covering the total area of the substrate to be exposed.
The U.S. Pat. No. 6,768,125 by the applicant/assignee presents a multi-beam maskless lithography concept, dubbed PML2 (short for ‘Projection Mask-Less Lithography #2’), that employs a pattern definition device comprising a number of plates stacked on top of the other, among them an aperture array device (aperture plate) and a deflector array device (blanking plate). These separate plates are mounted together at defined distances, for instance in a casing.
The aperture plate comprises an array of apertures which define a beam pattern, consisting of beamlets, to be projected on a target surface. Corresponding blanking openings on the blanking plate are associated with said apertures. Said blanking openings are located such that each of the beamlets traverses the blanking opening that corresponds to the aperture defining the beamlet respectively. Each blanking opening is provided with a deflection means that can be controlled by a blanking signal between two deflection states, namely, a first state (‘switched on’) when the deflection means has assumed a state in which particles passing through the opening are allowed to travel along a desired path, and a second state (‘switched off’) when the deflection means is deflecting particles transmitted through the opening off said path.
The deflection means comprise a set of beam blanking electrodes, basically a pair. The US 2005/0242302 A1 of the applicant/assignee proposes to form the electrodes around the blanking openings by perpendicular growth employing state-of-the-art electroplating techniques. This document proposes to form one of the electrodes, which is called ground electrode, so as to have a substantial height over the blanking plate and the other electrode, which is called blanking electrode. This is done in order to provide a better shielding of the blanking apertures against cross-talking and other unwanted effects.
There are several problematic issues in the use of pattern definition devices as described in prior art. The shielding of the blanking apertures against cross-talking, for instance, as well as a non-expensive way of producing said blanking device. In particular the forming of the electrodes employing perpendicular growth is a rather complex process. Additionally such electrodes are very sensitive to deformation and stress.
Moreover, electrodes that have a substantial height over the blanking plate impose a limitation of the electric field strength tolerable in the vicinity of the blanking plate (this is due to stray fields around the electrodes caused by the boundary conditions for the field lines). This represents a disadvantage particularly if the blanking plate is used as a part of a grid lens (as for example described in U.S. Pat. Nos. 5,801,388 and 6,326,632 by the applicant/assignee) where the side of the blanking plate comprising the electrodes is used to define the electrostatic potential of the negative (diverging) and/or positive (collecting) electrostatic lens.
In prior art the pattern definition means comprises at least two different plates for comparably high integration density of apertures and deflectors, namely an aperture plate used to form the shape of the beams and absorb the majority of heat load imposed by the incoming beam, and a blanking plate used as deflector array plate. Highly accurate alignment between the two or more plates and excellent alignment towards the direction of the incoming beam is required.